This invention relates to an electric shaver in which a rotational speed is optimally controlled during shaving, and more particularly, to an electric shaver that can shave people with beards having beards ranging from thin to thick under optimum conditions.
An electric shaver with no motor rotational speed control increases rotational speed under no load and decreases rotational speed under load. This type of electric shaver rapidly rotates its motor under no load wasting electric power. Wasteful use of electric power can be avoided by reducing no load rotational speed. To realize this, an electric shaver is known that controls motor rotational speed. Such an electric shaver is provided with a motor rotational speed sensing means. The motor rotational speed is controlled to a constant speed by the motor rotational speed sensing means and a motor rotation control means.
This type of electric shaver can prevent the wasteful use of electric power under no load conditions. However, it cannot regulate rotational speed in an optimal fashion according to the user's beard thickness. In the case of a thin bearded person, shown in FIG. 10(a) since the motor is driven at a constant rotational speed, whiskers are not guided into the shaver well. In addition, there is also a problem of susceptibility to razor burn after shaving. Since the rotational speed is maintained constant during shaving, as shaving progresses the same problems of poor whisker guidance and razor burn exist when used by a thick bearded person shown in FIG. 10(b).
To solve these problems, the present inventor developed an electric shaver to change motor rotational speed according to beard conditions (U.S. application Ser. No. 808,431, filed Dec. 16, 1991, now U.S. Pat. No. 5,274,735). In this electric shaver, motor load current is sensed to control rotational speed. When motor load current becomes smaller, motor rotational speed is reduced. Motor load current decreases when the amount of whiskers cut by the blades decreases. For this reason motor rotational speed decreases as shaving progresses. As motor rotational speed decreases during shaving, whiskers are guided into the shaver better for a cleaner shave. Razor burn is also reduced. This electric shaver has the characteristic that at first motor rotational speed is high and whiskers are easily cut (rough shaving), and near the end of shaving motor rotational speed is low (finishing).
In this type of electric shaver, motor load current is sensed and motor rotational speed is controlled immediately after that. At the beginning of shaving many whiskers are cut by the blades, motor rotational speed is large, and consequently motor rotational speed is increased. As shaving progresses, the number of whiskers cut by the blades decreases and motor rotational speed is reduced. However, in the practical application of the electric shaver, the face is not shaved over its entire area at one time. The entire face is shaved by repetitive rough shaving and finer finishing part by part.
FIG. 1 shows motor load current during shaving. As shown in this figure, load current has an overall decreasing trend while increasing and decreasing. Therefore, motor rotational speed also has an overall decrease with small increases and decreases. FIG. 2 shows changing motor rotational speed during shaving. As shown in this figure, motor rotational speed is varied over a given range. In FIG. 2, motor rotational speed of the electric shaver is controlled over a range from 6000 rpm to 7500 rpm.
Since the rotational speed of this electric shaver decreases as shaving progresses, razor burn protection and whisker guidance into the blades can be improved, but when used by a thick bearded person cutting ability is lacking, and when used by a thin bearded person razor burn can still occur. In particular, when rotational speed is adjusted for thick bearded people, razor burn increases for thin bearded people, and when rotational speed is adjusted for thin bearded people, cutting ability becomes worse for thick bearded people.
The present invention was developed to solve these problems, and it is thus a primary object of the present invention to provide an electric shaver with rotational speed controlled according to the beard that can shave both thick bearded people and thin bearded people under optimum conditions.
The above and further objects and features of the invention will be more fully apparent from the following detailed description with reference to the accompanying drawings.